The invention relates to a target plate for positioning components and a corresponding optical system.
In the prior art, the positioning and alignment of workpieces, components or construction machines is frequently effected by means of optical systems which provide the advantages of fast, accurate and non-contact measurements. The positioning can be effected, for example, by a position determination by the system, but the positioning is often also carried out “directly” relative to the visible optical radiation emitted by a transmitter. Thus, a laser beam for producing a reference axis is emitted, for example, by means of a positioned and aligned laser transmitter or a reference plane is defined, for example by means of a rotating laser. For determining the position or for visualizing the radiation, active or passive target elements are generally used.
In pipeline construction, too, optical systems, generally laser reference systems comprising canal construction lasers and target plates, are preferably used for accurate laying of the pipes. The alignment of the laser beam is often carried out relative to the gravity corer so that such laser devices are generally provided with a tilt sensor. The laser is accurately aligned or is aligned concentrically with the pipe in the starting shaft. By means of the laser, it is then possible to produce a reference beam as a reference axis for—further—pipes to be laid. For this purpose, a target plate is inserted into the pipe. The target plate is mounted concentrically on or in the pipe, at that end of the pipe facing a worker, opposite the starting shaft. If the laser reference beam strikes the center of a—generally imprinted—target mark of the target plate, the pipe is correctly positioned and aligned.
The laying of pipes takes place, as a rule, as follows: an excavator or crane operator lowers the pipe into a trench while a worker stands in or next to the trench and monitors the position and alignment of the pipe. He gives instructions to the operator and if necessary corrects the position of the pipe manually. The monitoring is effected on the basis of the reference signal on the target plate fixed on/in the pipe. If a collimated laser beam, as in devices of the prior art, is focused as a circle on the target plate, for example a focusing screen, the line of sight of the worker must be along the axis of the beam if he intends to detect the position of the pipe relative to the beam. The worker must therefore lie in the trench or constantly bend in order to align the pipe. In the case of inaccessible trenches, positioning by means of such a device is not feasible.
To enable a worker to receive a signal in the upright position or in a position remote from the longitudinal axis of the pipe, U.S. Pat. No. 5,095,629 describes a target and a target plate system which transmits incident laser radiation and deflects it into an aligned, conical angle range. For this purpose, structures are introduced into the surface of the target in order to direct the beam in a certain direction, for example in the direction of an upright worker. The structures of the surface of the target have a periodic lattice and therefore have the disadvantage of scattering the radiation with highly irregular brightness in a predetermined angle range. In certain directions or at certain angles, the worker is dazzled, whereas at directly adjacent angles the light spot is scarcely visible on the target plate. These brightness variations irritate the worker. Furthermore, such targets produce significant “side lobes” in directions not relevant for the application, which means that the transmitted beam correspondingly declines in intensity. Moreover, the formation of such a target having macroscopic structures is susceptible to environmental influences, such as dirt, moisture or mechanical abrasion. The surfaces must therefore be protected with a cover plate, so that a complicated design follows. Furthermore, the structure of the surface is designed for scattering radiation in a predetermined angle range; in the event of deviations from the corresponding position the beam projection is only weak or is no longer detectable at all.
DE 20 2004 000 503 U1 describes an optical system having a video camera, in which system the optical axis is aligned rigidly parallel to the longitudinal axis of a pipe to be laid, and the objective of which video camera points in the direction of the pipe openings. Arranged between the video camera and the pipe is a planar, optically partly transparent screen which is sharply focused by the video camera and is displayed on the video monitor of the camera. The operator can recognize the point of incidence of the laser on the screen and hence the alignment of the pipe to be laid. According to the possibility of remote observation by cable or radio, there is no longer any need for a person to be on site in the trench. However, the video camera is a complex sensitive optical device which is easily damaged during rough construction work. Moreover, the optical system at the pipe end requires an electrical supply, so that the use necessitates greater complexity. Furthermore, the system demands corresponding installation and operation by the workers on the building site, which, inter alia, can hinder the smooth course of the work.